1. Field of Invention
The present invention relates to an apparatus and method for the measurement of inductance. More precisely the present invention relates to an apparatus and method for the measurement of inductance of a wire-loop sensor in the presence of a vehicle moving in a traffic lane.
2. Description of the Related Art
It is well known in the prior art to measure the inductance of a wire-loop, which is part of the frequency determining circuit of an LCR oscillator, using frequency-counting techniques. Typically, the number of zero-crossings per time increment of the voltage across the terminals of the LCR capacitor, C, is counted. Because the frequency of the LCR oscillator is inversely proportional to the square root of the inductance, L, of the LCR circuit, changes in the inductance of the wire-loop are reflected in changes of the number of zero-crossings counted per time increment. The Class-C wire-loop oscillator described in U.S. Pat. No. 3,873,964 issued to Thomas R. Potter on Mar. 25, 1975 is typical of LCR oscillators used in the prior-art.
Another problem associated with the measurement of inductance in a wire-loop is crosstalk.